An SCR (Selective Catalytic Reduction) catalytic converter reduces the oxides of nitrogen by means of a reducing agent. As reducing agent, use is usually made of ammonia (NH3) or urea which is injected directly into the exhaust-gas flow upstream of the catalytic converter. Furthermore, the injected ammonia can be stored in the catalytic converter at low temperatures, which ammonia is then desorbed at high temperatures. In contrast, at relatively high temperatures of the substrate, the efficiency of the NOx conversion is determined substantially by the molecular ratio of ammonia to NOx at the inlet to the SCR catalytic converter.
The ammonia can be dosed, in aqueous solution, directly into the exhaust-gas flow above the SCR catalytic converter. The maximum storage capacity for the ammonia is dependent substantially on the size and the design of the SCR catalytic converter and on its temperature. Both the ammonia slippage downstream of the SCR catalytic converter and also the level of converted NOx are subject to disturbances caused by errors in the modeling of the ammonia storage level in the catalytic converter and also by uncertainty in the NOx emissions upstream. Further imponderables arise in that the actual level of injected ammonia cannot be determined exactly on account of contamination of the injection nozzle, and in that depositions of NH3 may occur in the exhaust line. Thus, uncertainties can affect NOx and ammonia estimates.
The present description may improve the efficiency of the conversion of SCR catalytic converters. Said improvement may be achieved according to the description by way of the features of the claims.
The inventor herein has recognized the above-mentioned limitations and has developed a method for adapting an SCR catalytic converter for a vehicle exhaust system, comprising: supplying an adaptation signal to a kinetic model and adapting an amount of stored reducing agents via of the adaptation signal, and adapting a reducing agent release amount via of a remainder of the adaptation signal, and adapting a total rate of a reducing agent storage via a storage adaptation rate generated from subtraction of the reducing agent release amount from the adaptation signal, conversion of a reducing agent concentration into a mass throughput, division by the maximum storage capacity and sign reversal; and adjusting an engine actuator in response to the stored amount of reducing agents, the reducing agent release amount, or the total rate of reducing agent storage.
By providing individual adaptation of stored reductants, reductant release rate, and reductant storage rate, it may be possible to improve output of a kinetic module that tracks reductant storage and use in a vehicle exhaust system. In one example, the reductant storage and usage may be determined via NOx sensors positioned upstream and downstream of an emissions device such as a SCR so that transient changes in reductant and NOx can be considered and accounted. Engine actuators such as fuel injectors and EGR valves may be adjusted in response to reductants so that increased engine emissions may be avoided.
The present description may provide several advantages. Specifically, the approach may reduce engine emissions via improving estimation of ammonia stored and consumed in an exhaust system. Further, the approach may be useful for reducing the amount of ammonia used in an exhaust system to reduce NOx. Further still, the approach may help to reduce emissions of ammonia from a vehicle via providing an improved estimate of ammonia stored in a SCR.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.
The drawings included herein serve merely for the explanation of the description, and do not restrict the description. The drawings and the individual parts are not necessarily drawn to scale. The reference symbols that are common to more than one figure are used to denote identical or similar parts between different figures.